It was long back that the concept of cell came in existence, when the Englishman Robert Hooke (1665) first saw them in a piece of cork under his primitive microscope. He coined the term cell (L.cella = hollow space). Later, in the year 1839 two scientists M.J.Schleiden and Theodor Schwann formulated their 'cell theory' or cell doctrine'. According to this theory all the living organisms are composed of cells and cell products.
The present day concept of cell is resultant of findings made by several investigators from time to time by applying better techniques. Electron microscopy reveals a better understanding of components of the cell.